Assuming you haven't read through it already, the best
startingpoint for you is on this site, read the pages Jim
has taken the trouble to put together at...
...if you follow his advice and the tips left on this BBS
you won't go far wrong. Try to avoid the FONT tags and make
good use of style sheets.
Re: your question about secondary domain names, the SE's
will not penalize you for it, but you will not get any
benifit if their pointing at exactly the same stuff.
As far as spam goes, use your head and avoid delibarate
repartition of data. As far as I know the limit for
repeating keywords in your META tags is 3 times.
If you want to get your site to the top of the SE results
(assuming its not amazingly specilised) you have to get
links to your site from other pages...
Hope this all helps...